Unfortunately many books, training manuals, and even FAA documents give a false image of the Victor Airways. They are usually depicted as long boxes with a flat top and a level bottom. In fact they don’t look much like that at all.
The airway is 8 nautical miles across — 4 on either side of the centerline. A Victor Airway is Class E, controlled airspace. The airway is a course between two VOR stations. To fly the airway, the pilot tracks outbound on the VOR radial that has been designated as the airway centerline. Eventually the aircraft gets halfway between the VORs that make up the airway. At the halfway point the pilot stops tracking away from the VOR that is behind and starts tracking inbound to the VOR that is ahead. The inbound radial is then the airway centerline. The outbound radial and inbound radial are not always reciprocals — this is because each VOR is aligned to magnetic north and each VOR station has a slightly different variation. Only the centerline of the airway is shown on a sectional chart with a blue solid line. The airway itself is much wider than the line on the chart.
The top of all Victor Airways is 18,000 feet above Sea Level, so the top of the airway is a flat surface that is parallel with Sea Level. The bottom of the airway however is not flat. The underside of the airway is always 1,200 feet above the terrain, so the bottom of the airway will have a ragged surface that is the exact duplication of the surface below. I live near Sea Level so the airways in my area are tall. They start at around 1,500 feet MSL and go up to 18,000 feet MSL — over three miles tall! But when a Victor Airway crosses over high terrain the bottom of the airway rises with the land. In the Rocky Mountains there are places where the bottom of the airway is at 12,000 feet MSL, but the top remains at 18,000 — which makes the airway in that area only about one mile tall and still eight nautical miles wide.
Look at Victor Airway 121 (V121) between the North Bend VOR and the Roseburg VOR in Oregon. Flying V121 from North Bend to Roseburg you would track outbound from North Bend on the 093-degree radial. The VORs are 38 nautical miles apart — we know that from the box with the number 38 at the halfway point. So, when we get approximately 19 miles out from North Bend, we will switch over and track inbound to Roseburg on the 272 degree radial (notice 093 and 272 are not reciprocals). All across V121 between North Bend and Roseburg the top of the airway is 18,000 feet, but as you can see from the chart symbols, the ground below V121 is not level. The airway starts at near Sea Level, but before arriving at Roseburg it crosses rising terrain and one mountain ridge. The chart shows terrain elevations along the airway as high a 2,866 feet. So the airway would not look like a square oblong box of airspace. It would look more like the image below.
OVERLAPPING AIRSPACE AND AIRWAYSThe underside of the airway never gets any closer or farther away from the ground than 1,200 feet. As the terrain rises, so does the base of the airway — but the top never changes, so the airway gets squeezed thinner as the ground comes up. Sometimes, things get a little more complicated.
The image below is a blow up of the airspace around North Bend where V121 begins. In addition to a Victor Airway, North Bend has Class E to the surface (magenta dash line). Just outside the magenta dash line is an area of Class G at the surface — but inside the magenta shading, this Class G only goes up to 700 AGL. Outside the magenta shading the Class G extends up to 1,200 feet AGL. Over the top of all of that is V121 — the Victor Airway.
BOTTOM LINE: As a pilot you must develop a mental image of what airspace types actually look like. This especially includes enroute navigation using the Victor Airways.